What revision of the logic board in a macintosh 128k?

[MR. T]

Hi all,

as this is my first posting i like to introduce myself a bit. I'm Carlo from Germany and I'm an longtime Apple user.

I started with an Apple //c in 1990 and now I'm using a G4. I have a little collection of Apple II and Macintosh computers.

Recently I got a Macintosh with the 128k label on the back from ebay. The serial number states that the machine has been

manufactured in the 4th week of 1985. It' a model for the european market PS= 220V. The logic board is upgraded to 512k

(chips replaced by larger ones and a little circuitadded to the logic board). That was a little disappointing as I liked to have

an machine as original as possible. Next thing I discovered that it has the first revision of the logic board 820-0086-C.

I expected to find a later revision of the logic board.

So please can you tell me what revision of the logic board has to be in a "macintosh 128k".

Thanks and greetings from Bremerhaven, Germany

Carlo

 

[H3NRY]

I have a couple of early 128K boards; both are marked 820-0086-C in the top copper layer, and printed with a © 1983 date. Later 128K/512K boards do not need the little decoder board, as the additional address decoder is already on the board.

Welcome aboard.

 

[JDW]

Here are my 128k logic board photos, which show top and bottom and many angles. Click on the individual photos, then click on the little "All Sizes" button above the photo to see the large size. This board came out of a stock Macintosh 128k that was built in 1984.

Henry, I would appreciate it if you could pick on the my photos and then mark it with the "decoder board" you are speaking of. Or otherwise mark the location. (Are you speaking of the 7 holes shown in my photos between RP1 and C34? Someone named "Henry" mentioned this in the commentary section at the bottom of this Folklore page.)

 

[Mac128]

(Are you speaking of the 7 holes shown in my photos between RP1 and C34?

That is exactly right. There are many pictures on the forum of these mini-mux boards which allow the additional RAM to be decoded. The procedure is explained in great detail in Larry Pina's Macintosh Repair and Upgrades.

 

[H3NRY]

JDW, the pictures referred to show the decoder. Before there were little decoder boards made, people piggybacked an additional 7AS153 atop the one at F3 as in this photo:

http://homepage.mac.com/henryspragens/.Pictures/Macs/100_0398.JPG

http://homepage.mac.com/henryspragens/PhotoAlbum17.html

You might find this article interesting, too:

http://homepage.mac.com/henryspragens/PhotoAlbum16.html

And yes, it was me upgraded Andy's Mac to 1MB as mentioned at Folklore.com. We upgraded a lot of Apple engineers' Macs.

We also made unmodified 128Ks valuable by making them scarce.

 

[JDW]

Carlo (Mr.T), after reading your post again I see that you are expressing disappointment over not having a stock 128k. What I can say is that 128k logic boards are often sold on EBAY (in the USA at least) so you would have the opportunity of putting the logic board back in the stock condition that way. However, from a practical standpoint, you will find the 512k much more useful. I know I do. And if you have the original Apple 64k ROMs installed, then your Mac should also be fully compatible with even the oldest software that originally came out for the 128k machine.

Henry, I must say I found your photos and the magazine scans very interesting indeed! So you are Henry Spragens of Beck-Tech. (Perhaps I should have known this by now, but sometimes my head is fitting firmly in a hole in the ground.) That explains quite well your extensive electrical knowledge of these old compact Macs.

Perhaps this is a subject for another thread, but curiosity is killing me. As we all know, Levco and Dove ultimately became major players in the compact Mac memory upgrade market. In those early days, what challenges did Beck-Tech face in selling Mac memory upgrades against those competitors? And at what point did Beck-Tech call it quits?

I also came across this Aug 1985 InfoWorld review of Beck-Tech's MACMEGABYTES upgrade. The review mentions "Version 2" of the product included its own ROM in order to allow the use of the entire 1MB as system memory (versus 512k of RAM disk). Was your ROM 100% compatible with all software that worked on Apple's 64k ROM? And what happened to your upgrades when Apple's 128k ROM came on the scene?

Yet another question... Would you happen to still have a hi-rez version of the Beck-Tech Macintosh Logic Board Schematics? (Interestingly, the far right column of page 35 in the MICROTIMES July 1985 article you scanned mentions that another Mac schematic was created in MacPaint by IM Underground -- I'd love to see that.)

 

[H3NRY]

Beck-Tech's modified ROM was exactly the same as the original, except that in about a dozen places, Andy had hard-coded the screen address for 512KB of RAM, and those needed to be bumped up to the 4MB limit that the hardware allowed. When the 128K (Plus) ROM came along, it fixed the memory limits. A 512Ke could take a MacMegabytes card without any ROM changes and have a meg of system RAM. We were quite relieved when Apple released the 128K ROM upgrade. Of course it made everybody else's RAM upgrades work properly too, so we gained some, we lost a little. Apple's 128K ROMs are also 100% compatible with the 64K ROMs, so a Mac Plus will run all the early pre-release demos like Pepsi Caps or the first Alice, which aren't even Finder-compatible.

I have a Beck-Tech logic board poster around here someplace. I guess I should photograph it and post it. Too big for my scanner. I also have my original MacDraw schematics which the poster was done from as well as Phat's timing diagrams and PAL analysis. I'll dig them out and put them on dotmac. You'll need a classic Mac with MacDraw to open the files. I have the IM Underground stuff filed away someplace, and a 1986 Hackintosh I should probably take pictures of for history buffs. Phat and I weren't the only ones reverse-engineering the Mac.

Thanks for the pointers to the review and the schematic, JDW. I had forgotten those. My God, is there anything about the early Mac you don't know? 8-o

 

[MR. T]

Carlo (Mr.T), after reading your post again I see that you are expressing disappointment over not having a stock 128k. What I can say is that 128k logic boards are often sold on EBAY (in the USA at least) so you would have the opportunity of putting the logic board back in the stock condition that way.)[/i]

That's what i like to do, but I don't know what revision of the logic board belongs

to that mac. It has revision 820-0086-C of the logic board and was manufactured

in the 4th week of 1985, so i think case and logic board do not match.

As my question wasn't quite clear, I try again:

I like to know if one can determine by the label on the back of the macintosh case

or better by the serial number what revision of the logic board has to be in it.

The best would be a table like this:

case label__________Serial Number to Serial Number ______________Logic board rev.

macintosh__________Fxxxxxxxxxxxx to Fxxxxxxxxxxxx__________820-xxxx-x

macintosh 128k______________________________________________________________

macintosh 512k______________________________________________________________

 

[JDW]

Carlo, since my HyperDrive 20 Mac is a Macintosh 512k with the "512k" label on back and with a stock Macintosh 512k board that has never been swapped out or upgraded, I am happy to answer your question. First have a look at this web page and search for "820-0141-A". That is likely the PCB revision you are looking for and is exactly what I have, as shown in my photo here. That PCB revision was made to either be a 128k board or a 512k board, and there are two white silkscreen boxes on the top side of the PCB that are used to mark which board it is (either 128k or 512k). (That Chinese Mac web page also talks about revision 820-0086-F, but I cannot say much about that since I don't have one. Mac128 asked about this "F" variant in this old post. I see one currently on sale at WeLoveMacs though.)

So if you want to find a 128k board that is stock to your Mac's plastic housing, then you probably want 820-0141-A or the 820-0086-F. Perhaps someone more knowledgeable that I can tell you the difference between the two. But I don't think you are going to increase the value of your Mac though, whether you put a revision 820-0141-A board in there or a revision 820-0086-C board inside. The original 128k without the 128k badge on back is the original from 1984 and carries the most value.

Henry, I'm dying to have that MacDraw file!

 

[Mac128]

I like to know if one can determine by the label on the back of the macintosh case

or better by the serial number what revision of the logic board has to be in it.

The best would be a table like this:

The short answer is, not easily.

The long answer is this:

case label__________Serial Number to Serial Number ______________Logic board rev.

macintosh__________F35xxxxxM0001 to F4xxxxxxxxxxx__________820-0086-C/F (630-0101)

macintosh 128k__________F4xxxxxxM0001 to F5xxxxxxxxxxx__________820-0141-A (630-0101)

macintosh 512k/e__________F44xxxxxM0001 to F7xxxxxxxxxxx__________820-0141-A (630-0118)

The original Macintosh released in January 1984 came with 820-0086-C. I have several very early stock 128K Macs with these original boards. It may have been upgraded to the "F" revision prior to being discontinued sometime in October 1984. However, I have never seen any hard evidence of this board's existence, other than references. ALthough I have never seen any physical evidence, it is entirely possible the board configuration was upgraded from 630-0101, to 630-0101-"x".

In October 1984, this board was replaced with the 512K hybrid board. This board is identical in both the 128K & 512K/e. Again it is possible that late versions of these boards included a new revision letter for both the logic board (820) as well as the board configuration (630). But the first versions would have been as indicated. I have early examples of 512K and Ke Macs all of which came stock with these boards. As far as I know these boards were used until the last 512Ke was produced sometime in 1987, though I have never personally seen any 512Ke's manufactured that late.

There is no easy way to tell which serial number belongs to the "Macintosh" versus the "Macintosh 128K" since as far as I know there is no documentation as to exactly when the new badging appeared. Given the late manufacturing date of some of the original 128K labels, we know it did not happen at the same time the 512K was released but sometime after that, probably in 1985.

You may find some more detailed information in the M0001 Registry database.

THE BOTTOM LINE: If you are trying to obtain an original stock 128K logic board, an unmodified 820-0086-C/630-0101 is what you are looking for. The RAM chips should be labeled 64, NOT 256. Someone else may correct me, but I do not believe the earliest boards would not have Apple logos on the RAM chips either. There should be nothing at location E3 except 7 solder points. Also: to be truly stock and original it will NOT have a resister array added onto the 6522 VIA IC at D-15, added during most repairs to prevent a type of lock-up, which I believe Apple actually began adding at the factory in late '84. Also, note there was a ROM upgrade in late '84, sometime after the 512K was released as all of my '85 512Ks have the original ROM. So to be truly stock your ROMs should be 342-0220/1-A ©1983 variety, NOT 342-0220/1-B ©1984.

 

[JDW]

So to be truly stock your ROMs should be 342-0220/1-A ©1983 variety, NOT 342-0220/1-B ©1984.

Henry, since Beck-Tech read out the Apple ROMs to develop its memory upgrades, would you be able to tell us the code differences between Apple's 64k revision-A and revision-B ROMs?

 

[H3NRY]

Mr T, it's quite likely the motherboard in your Mac is the original, though upgraded to 512K. The original boards were shipped in 128Ks even after the Fat Mac 512K was introduced. Apple apparently had a lot of the older boards on hand. You would be correct to use either motherboard in your Mac. By the way, the code name for the Mac Plus was "Mr.T".

JDW, I've forgotten the difference between the 64K ROMs. It was something very minor to do with the ROM debugger IIR (we were hoping for a fix for >512K of RAM of course). There were also multiple 128K ROMs, going by the Low-High names of Loud-Harmonica, Lonely-Heiffer, etc. and the difference there was mostly in handling SCSI boot protocol. The first Plus ROMs wouldn't boot a lot of drives, but disk drive manufacturers couldn't count on a customer having the fixed ROMs because Apple didn't do ROM upgrades.

 

[Mac128]

I've forgotten the difference between the 64K ROMs. It was something very minor to do with the ROM debugger IIR (we were hoping for a fix for >512K of RAM of course).

JDW, I brought this up here before.

My understanding is that it specifically addresses a revised stepper motor in the Sony 400K drives. There were two basic types of disk drives: Early Sony model OA-D34V (shipped with ROM version 342-0220/0221-A).

Later Sony models OA-D34V-02 or OA-D34V-22. These models had a new insert/eject mechanism (shipped with ROM version 342-0220/0221-B, these drives were incompatible with ROM version A).

There may have been some other minor changes, but this seems to be the primary motivation for it.

Henry do you mean the ROM interaction with Macsbug? As the 64K ROM did not have a debugger built-in like the 128K ROM.

Of course Jobs was still firmly driving the boat at that time, so there would have been no chance for a >512K RAM fix. I'm sure Jobs even fought the stepper motor fix, since it only proved him wrong.

 

[zastin17]

JDW, I brought this up here before.

My understanding is that it specifically addresses a revised stepper motor in the Sony 400K drives. There were two basic types of disk drives: Early Sony model OA-D34V (shipped with ROM version 342-0220/0221-A).

Later Sony models OA-D34V-02 or OA-D34V-22. These models had a new insert/eject mechanism (shipped with ROM version 342-0220/0221-B, these drives were incompatible with ROM version A).

There may have been some other minor changes, but this seems to be the primary motivation for it.

Henry do you mean the ROM interaction with Macsbug? As the 64K ROM did not have a debugger built-in like the 128K ROM.

Of course Jobs was still firmly driving the boat at that time, so there would have been no chance for a >512K RAM fix. I'm sure Jobs even fought the stepper motor fix, since it only proved him wrong.

For 400k drives. I found some weird inconsistencies. My 0A-DV-22 has a top board just like the original Non 22. And works perfectly on 128k A roms. 342-0332-A and 342-02290-A. My other DV-22 has a different top motor board, a newer stepper motor, and has issues with A roms.

Both drives are OA-DV-22, but are both built differently and different stepper motors. One with a flat label, and one with a Round label on the stepper. One works with A rom, one does not initialize properly but does work on my Macintosh Plus from 1985. Both labeled OA-DV-22

The newer DV-22 drive has less caps on the top board, and sensor wires are routed differently aswell. Looks like the older one more or less. But both labeled OA-DV-22. Does have the new eject mechism.

Macintosh week 27 if that helps came with old-style DV-OA-22 drive and A roms.